The present invention relates to a hygroscopic web, and more particularly, to a special belt for machines producing corrugated cardboard. Belts for this type consist of one or several layers of great tensile strength which stretch little, and are covered at least on one side by outer layers.
Belts of this type have not only to transport corrugated cardboard, but also serve the purpose to absorb the moisture which is vaporized during drying, and is part of the glue adhering to the corrugated cardboard. Furthermore belts serving the above-explained purpose must be capable to distribute the pressure of the loading rollers of the apparatus uniformly to the corrugated cardboard which is to be adhesively connected, so that a sufficient and uniform adherence is obtained.
A belt or web of this type is described in the DGBM 1,964,682. In this transporting belt, the warp threads in the outer layers of the web consist of cotton threads, while the inner layer consist of a synthetic material. Originally, woven cotton belts were used, and it has also been proposed to use webs woven of synthetic material, or needled felts consisting of synthetic fibers, in order to overcome the disadvantages of cotton.
However, it has been found that in the webs of the prior art, the outer layers are worn off too quickly. Research by the inventors resulted in the recognition that the great wear is caused in the first place by low temperature resistance and abrasion resistance of cotton. Furthermore, the length of cotton webs is not constant and to the reduction of the strength of the cotton fibers, due to continuous effects of moisture, heat and tensile forces.
Belts according to the prior art consisting of synthetic yarns or of felt, consisting of synthetic fibers, have the disadvantage that they show undesirable properties due to surface smoothness and surface hardness, obtain a high electrostatic charge, and have unsufficient transverse tensile strength, transmit the pressure of the printing rollers only as line pressure and not as area pressure, and do not run as quietly as desired.